In a generally adopted method of drilling processing of a laminate or a multilayer board for use as a printed wiring board material, one laminate or multilayer board or a plurality of laminates or multilayer boards stacked are provided, and on the uppermost surface thereof, a sheet as an entry board is stacked which is a metal foil of aluminum or the like alone or includes such a metal foil and a resin composition layer formed thereon (hereinafter, such a sheet is usually referred to as “entry sheet for drilling”, or also simply referred to as “entry sheet”), followed by performing hole boring processing. A “copper-clad laminate” is generally used as the laminate in many cases, but a “laminate” with no copper foil on the outer layer thereof may also be used.
In recent years, progress of high density, enhancement in productivity and cost reduction, as well as enhancement in reliability has been demanded of a laminate or a multilayer board as a printed wiring board material, and there has also been demanded hole boring processing of high quality such as enhancement in hole position accuracy. In response to such demands, for example, Patent Document 1 has proposed a method of hole boring processing, in which a sheet including a water-soluble resin such as polyethylene glycol is used. In addition, Patent Document 2 has proposed a lubricant sheet for hole boring, in which a water-soluble resin layer is formed on a metal foil. Furthermore, Patent Document 3 has proposed an entry sheet for hole boring, in which a water-soluble resin layer is formed on an aluminum foil with a thermosetting resin thin film formed thereon.
Moreover, an entry sheet for hole boring in which a solid lubricant is used has also been proposed. For example, Patent Document 4 has proposed an auxiliary plate material for hole boring, in which the auxiliary plate material includes a lubricant layer, a composite material including a nanostructured powder (of tungsten disulfide or the like) and a solid, wear-resistant lubricant layer that is a highly thermal conductive compound, and a supporting agent. Patent Document 5 has proposed an entry sheet for hole boring which has a water-soluble resin layer containing zinc molybdate and molybdenum trioxide.